The combustion byproducts of hydrocarbon fuels primarily include nitrogen (N2), carbon dioxide (CO2), water (H2O), carbon monoxide (CO), unburned hydrocarbons (UHC), oxides of sulfur (SOx), particulate (soot), oxides of nitrogen (NOx), elemental mercury (Hg), oxides of mercury (Hg(II)) and hydrogen chloride (HCl). The items, CO, CO2, Hg, Hg2, HCl, UHC, SOx, particulate and NOx are unwanted and undesirable. These pollutants are referred to as criteria pollutants and many regulatory agencies around the world have established guidelines for their control. CO is a gas that is an intermediate product of combustion of hydrocarbon fuels. UHC often results from poor fuel atomization or quenching of the combustion process by the combustion cooling air film or by high levels of water or steam injection. Oxides of sulfur are formed when sulfur is present in the fuel during combustion. SOx forms over a wide range of combustion temperatures and cannot be controlled in the combustion process itself. Hence, SOx formation either must be prevented from occurring by limiting sulfur in the fuel or else the SOx that is created must be removed from the exhaust stream by wet scrubbing or sorbent injection. Particulate matter (i.e., soot or smoke) results from the combustion of liquid fuels/air ratios in the combustion primary zone. NOx, by virtually unanimous agreement, is considered a primary contributor to visible pollution and deteriorating air quality. The reduction of NOx has become the major focus of air quality regulations throughout the world in efforts to improve air quality.
Reducing NOx along with other unwanted pollutants from fossil fuel-fired turbine exhaust gas is an important process for atmospheric and environmental protection on a global scale. Natural-fired, oil-fired, diesel-fired and biofuel-fired turbines produce tons of NOx per year, along with other unwanted pollutants such as SOx, HCl, mercury and particulate.
Concerns over the future effects of global climate change are increasingly leading to the desire to control and reduce carbon dioxide (CO2) emission into the atmosphere. CO2 originates from a variety of sources, many of which involve the combustion of an organic fuel such as coal, natural gas, gasoline, fuel oil, and methane. Specifically, combustion processes that are used for the generation of electricity and/or heat are a significant source of CO2.
Capturing and reusing waste energy is another important factor in the operation of the fossil fuel fired turbine plant. To this end, many plants employ heat recovery steam generators (HRSG) that capture most of the waste heat and produces steam to increase the operational output of the plant. However, there is still approximately 10% of the waste heat that escapes to atmosphere that can be captured and reused in the plant to increase the efficiencies of the operations of the fossil-fired fuel turbine plant.